1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member having an intermediate layer.
2. Description of the Prior Art
Basically an electrophotographic photosensitive member is constructed of a substrate and a photosensitive layer. However, it is effective to interpose an intermediate layer between the substrate and the photosensitive layer, for enhancing the adhesion of the photosensitive layer to the substrate, improving the workability of coating which forms the photosensitive layer, protecting the substrate, covering defects on the substrate, protecting the photosensitive layer from electric breakdown, improving the ability to inject an electric charge from the substrate into the photosensitive layer, and so forth.
It has hitherto been known that the intermediate layer may be prepared of poly(vinyl alcohol), poly(vinyl methyl ether), poly-N-vinylimidazole, ethylcellulose, methylcellulose, ethylene-acrylic acid copolymer, casein, gelatin, polyamide, or the like.
Electrical properties are cited as primary examples of the properties required for the intermediate layer. Since this layer is used in an electrophotographic photosensitive member, it is important that the layer has no adverse effect on the electrophotographic characteristics of the photosensitive member. Therefore the electric resistance of the layer needs to be low. If the resistance is high, potential will be applied to a subbing layer when the photosensitive member is electrically charged, and this may cause so-called fogging, as one effect of the residual potential on the image.
Further, the electric resistance is required to be unaffected by environmental changes, particularly by the change in atmospheric humidity. For instance, when the electric resistance is raised with a decrease in atmospheric humidity, fogging will be caused.
In order to cover defects on the substrate, the intermediate layer is also required to have such a coating property as to hide the defects effectively. That is, the intermediate layer needs to produce no defect unto itself that are traceable to a defect on the substrate. The intermediate layer, when defects on the substrate are projections, needs to cover and hide them with its own surface kept flat and smooth and when defects on the substrate are hollows, needs to fill up and hide them similarly.
Although such properties as mentioned above are required for the intermediate layer, these requirements have not been fulfilled with the prior art intermediate layer composed of a single resin.